The "ANR8782E Volume 500174 could not be accessed by library ..." is your
clue.  This message is issued when an ERA code is received from the library
manager indicating that it can't access the volume (ERA 64, 67, 6B, or 75),
so it's not ADSM per se.

What you can do to further diagnose this is use mtlib and query the
volume directly, ie.

   mtlib -l/dev/lmcpX -qV -V<uppercase volid>

and this should return the same ERA that ADSM is getting along with a
hopefully explanation.  You can also query the volume in the database
on the Library Mgr console.  Then see you CE about why the volumes are
getting misplaced/lost/whatever.

Craig Bell